I picked up a little day-by-day desk calendar on sale for my son - okay, it's not as cheesy as it sounds, being April already and all. It's one of those little origami calendars. Each day there is a new paper - with instructions on how to create something nifty on the back simply by folding the paper. The paper is decorated in a pretty color.
This works great, because he wants to sit down and do a whole month's worth of the origami anyway, and he normally saves the paper (because the instructions are on the back) and makes the creations with his own paper.
I found some great scrapbooking paper at Costco for him - it's perfectly square already, so no cutting required. And in great, bright colorful designs!
I introduced origami to my son a few years ago - he is very bright and just couldn't find enough to do, so I figured this would be a good activity for him. He just loves it! He is an expert at it (has been for years) and can understand complicated designs. He's also modified designs and created his own.
He wants to be an engineer - I think this is a good sort of hobby for this kind of brilliant little boy.